The present invention relates to an auto-focus regulating method for video cameras and device thereof.
Generally, the auto-focus regulating method for video cameras is classified roughly into an active method by infrared ray distance calculation or ultrasonic wave distance calculation and a passive method by image sensing or image detecting.
According to the active method, infrared rays or ultrasonic waves illuminate an object to be photographed, and the reflected wave is received by a sensor installed in a camera so that the distance between the camera and the object can be measured, thereby driving the focus mechanism of lens so that the focus is regulated in accordance with the measured distance. The active method has advantages in that the focus can be adjusted at a close distance and the performance is high. However, it has a disadvantage in that it requires a separate distance calculator.
The image detecting method of the passive method calculates the distance between two images formed by two fixed reflecting mirrors and an object and drives the focus mechanism.
In contrast, a high frequency detecting method calculates the resolution level of an object by extracting the high frequency component from the image signal and then drives the focus mechanism so that the resolution level of the object becomes maximum. That is, the in-focus state is the state by which the maximum resolution level of an object is achieved. The high frequency detection method uses the maximum high frequency component of the image signal.
Recently, such a high frequency detection method has been widely employed since a separate distance calculator is not needed as in the active method, nor is a mechanical device necessary, unlike the image detecting method.
However, in the image detecting method, it is difficult to regulate the focus normally since, in the case of an object or a background having a low illuminance or an obscure contour, the high frequency component is reduced abruptly.
Also, the image detecting method has been attributed with a disadvantage in that focusing a position on a screen is impossible since the focus should be regulated so that the overall resolution level is improved.